Optical disc drive for controlling reproduction of an optical disc having a plurality of data layers

ABSTRACT

When recording or reading an optical disc having plural data recording layers, which data recording layer the light spot is focused on is detected to improve playback signal quality and signals written to the layer on which the light spot is focused are read more reliably. A convergent lens converges the laser beam on the optical disc, and a focus controller controls the focal point of the laser beam on the data layer. A tracking controller positions and tracks the focal point of the laser beam converged by the convergent lens on a track of the optical disc. A photodetector detects the reflected laser beam from the disc. A convergence detector then detects the convergence state of the laser beam emitted to the plural data recording layers. Based on output from the convergence detector, the laser driver is controlled to separately set beam power appropriately for each of the plural data layers of the disc during playback.

TECHNICAL FIELD

The present invention relates to an optical disc to which information isrecorded by emitting a laser beam to the optical disc surface, and to anoptical disc drive for using the optical disc.

BACKGROUND ART

Optical disc drives have been actively developed as a way to record andreproduce large volumes of data. Various approaches have been taken toincrease the recording density. Phase change optical disc media drivesthat use the ability to change the recording layer between crystallineand amorphous states are one such approach.

Phase change optical disc drives heat the recording thin film formed onthe disc substrate by emitting a laser beam, thereby causing a change inthe crystalline structure of the thin film to record and eraseinformation. Amorphous marks and crystalline spaces between the marksare formed on the optical disc by emitting the laser beam at a peakpower level to convert crystalline parts of the recording film to anamorphous state, or at a bias power level to convert amorphous parts toa crystalline state. Reflectance is different in the recorded marks andspaces. When a light spot is focused on the optical disc, differences inmark and space reflectance are detected as a signal, which is thendecoded to read the information.

Land and groove recording techniques enable recording marks and spacesto both the land tracks of the guide grooves on the disc and the groovetracks therebetween.

Address prepits are formed also at the factory when the guide groovesare formed in the disc. These address prepits identify specificlocations (addresses) on the disc, and recessed pits and lands formed ata constant interval along the tracks. Address information is recorded bycontrolling whether the pits are formed or not and changing the lengthof the pit sequence.

A conventional optical disc drive is shown in FIG. 2. Shown in FIG. 2are the optical disc 201, semiconductor laser 202, collimator lens 203for converting the light beam emitted from the semiconductor laser to aparallel beam, beam splitter 204, convergent lens 205 for focusing thelight beam on the optical disc surface, collective lens 206 forcollecting the light beam reflected and diffracted by the optical disconto a photodetector 207, the photodetector 207 for detecting the lightcollected thereon by the collective lens, playback signal operator 208for arithmetically calculating the output voltage of the photodetector,focus controller 209 for controlling the focal point of the light spoton the optical disc surface, tracking controller 210 for controlling theposition of the light spot to the tracks on the optical disc, actuator211 for moving the convergent lens, laser drive unit 212 for driving thesemiconductor laser, and signal processing unit 215.

A problem with this conventional configuration is that when data isrecorded to or read from an optical disc having plural data layersaccessible from one side of the disc and addresses are read from prepitsformed in a second data layer (a layer deeper from the disc surface thanthe first data layer), absorption and reflection by the first (surface)layer causes a loss of power in the beam reaching the second layer. Thisloss is proportional to the transmittance of light through the firstlayer.

Light reaching the second layer is then reflected and diffracted by theaddress prepits in the second layer, passes back through the firstlayer, and reaches the photodetector. The amount of light in the beamreaching the photodetector is proportional to the square of the firstlayer transmittance and the reflectance of the second layer.

If, for example, the transmittance of the first layer is 50% and theamount of light in the beam emitted from the laser and incident on thefirst layer is 1, the amount of light that passes the first layer,reaches the second layer and is diffracted by the second layer, thenpasses through the first layer again and reaches the photodetector willbe 1*(0.5*0.5)−R2=0.25−R2 where R2 is the reflectance of the secondlayer. In an optical disc in which the optical characteristics arecontrolled so that the reflectance difference (ΔR) between spaces andrecording marks in the first and second layers is the same, the amountof light diffracted by the prepits and returning to the photodetector isdependent upon the transmittance of the first layer and the reflectanceof the second layer. If the transmittance of the first layer is low orthe reflectance of the second layer is low, a difference occurs in thesignal amplitude from the address prepits in the first and secondlayers. This can make it difficult to accurately read the addressinformation from the prepits in the second layer.

SUMMARY OF INVENTION

The present invention is directed to a solution for the aforementionedproblems. An object of this invention is to detect the recording layeron which the light spot is focused by means of a convergence statedetection means, improve read signal quality by means of a signalquality boosting means so as to achieve optimal signal quality for therecording layer on which the light spot is focused, and thereby improvethe playback signal quality for address signals reproduced from prepitsin the second recording layer.

To resolve the problems of the prior art and achieve the above objects,an optical disc according to the present invention is an optical dischaving preformed identification signals indicating disc positions and aplurality of data layers for recording data signals using a local changein an optical constant or physical shape effected by light beam emissionto recording tracks where both spiral or concentric groove tracks andland tracks between the groove tracks formed on each data layer arerecording tracks where the identification signals consist of peak andvalley prepits of different optical depth or height on the plural datalayers.

An optical disc drive according to the present invention has an opticaldisc having plural data layers; a laser drive means for driving asemiconductor laser; a converging means for converging a light beam onthe optical disc, the light beam being light output from thesemiconductor laser driven by the laser drive means; a focus controlmeans for controlling a focal position of the convergence point of thelight beam converged by the convergence means on the optical disc; atracking control means for positioning the convergence point of thelight beam converged by the convergence means on a track of the opticaldisc; a photodetection means for detecting reflection of the convergedlight beam from the optical disc; and a convergence detection means fordetecting convergence of the light beam emitted to the plural datalayers of the optical disc; wherein the optical disc drive controls thelaser drive means based on output from the convergence detection means,and sets light beam emission power when reading the disc separately forthe plural data layers of the optical disc.

An optical disc drive according to a further aspect of the presentinvention has an optical disc having plural data layers; a laser drivemeans for driving a semiconductor laser; a converging means forconverging a light beam on the optical disc, the light beam being lightoutput from the semiconductor laser driven by the laser drive means; afocus control means for controlling a focal position of the convergencepoint of the light beam converged by the convergence means on theoptical disc; a tracking control means for positioning the convergencepoint of the light beam converged by the convergence means on a track ofthe optical disc; a photodetection means for detecting reflection of theconverged light beam from the optical disc; a gain control means forcontrolling changing the gain of output from the photodetection means;and a convergence detection means for detecting convergence of the lightbeam emitted to the plural data layers of the optical disc; wherein theoptical disc drive controls the gain control means based on output fromthe convergence detection means, and sets the output voltage of thephotodetection means when reading the disc separately for the pluraldata layers of the optical disc.

An optical disc drive according to a further aspect of the presentinvention has an optical disc having plural data layers; a laser drivemeans for driving a semiconductor laser; a converging means forconverging a light beam on the optical disc, the light beam being lightoutput from the semiconductor laser driven by the laser drive means; afocus control means for controlling a focal position of the convergencepoint of the light beam converged by the convergence means on theoptical disc; a tracking control means for positioning the convergencepoint of the light beam converged by the convergence means on a track ofthe optical disc; a photodetection means for detecting reflection of theconverged light beam from the optical disc; an equalization controlmeans for controlling the equalization characteristics of photodetectionmeans output; and a convergence detection means for detectingconvergence of the light beam emitted to the plural data layers of theoptical disc; wherein the optical disc drive sets the equalizationcharacteristics for each of the plural data layers based on output fromthe convergence detection means.

An optical disc drive according to a further aspect of the presentinvention has an optical disc having plural data layers; a laser drivemeans for driving a semiconductor laser; a converging means forconverging a light beam on the optical disc, the light beam being lightoutput from the semiconductor laser driven by the laser drive means; afocus control means for controlling a focal position of the convergencepoint of the light beam converged by the convergence means on theoptical disc; a tracking control means for positioning the convergencepoint of the light beam converged by the convergence means on a track ofthe optical disc; a photodetection means for detecting reflection of theconverged light beam from the optical disc; and a convergence detectionmeans for detecting convergence of the light beam emitted to the pluraldata layers of the optical disc; wherein the optical disc drive sets thefocal position for each of the plural data layers based on output fromthe convergence detection means.

An optical disc drive according to a further aspect of the presentinvention has an optical disc having plural data layers; a laser drivemeans for driving a semiconductor laser; a converging means forconverging a light beam on the optical disc, the light beam being lightoutput from the semiconductor laser driven by the laser drive means; afocus control means for controlling a focal position of the convergencepoint of the light beam converged by the convergence means on theoptical disc; a tracking control means for positioning the convergencepoint of the light beam converged by the convergence means on a track ofthe optical disc; a photodetection means for detecting reflection of theconverged light beam from the optical disc; and a convergence detectionmeans for detecting convergence of the light beam emitted to the pluraldata layers of the optical disc; wherein the optical disc drive sets thetracking position for each of the plural data layers based on outputfrom the convergence detection means.

An optical disc drive according to a further aspect of the presentinvention has an optical disc having plural data layers; a laser drivemeans for driving a semiconductor laser; a converging means forconverging a light beam on the optical disc, the light beam being lightoutput from the semiconductor laser driven by the laser drive means; afocus control means for controlling a focal position of the convergencepoint of the light beam converged by the convergence means on theoptical disc; a tracking control means for positioning the convergencepoint of the light beam converged by the convergence means on a track ofthe optical disc; a tilt control means for controlling tilt of theconvergence point of the light beam converged by the converging means atthe optical disc surface; a photodetection means for detectingreflection of the converged light beam from the optical disc; and aconvergence detection means for detecting convergence of the light beamemitted to the plural data layers of the optical disc; wherein the tiltposition is set for each of the plural data layers based on output fromthe convergence detection means.

Other objects and attainments together with a fuller understanding ofthe invention will become apparent and appreciated by referring to thefollowing description and claims taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an optical disc drive according to thefirst and fifth embodiments of the present invention;

FIG. 2 is a block diagram of an optical disc drive according to theprior art;

FIG. 3 shows the configuration of an optical disc recorded andreproduced by an optical disc drive according to a first embodiment ofthe present invention;

FIG. 4 is a flow chart used to describe the recording and playbackprinciple of an optical disc drive according to a first embodiment ofthe present invention;

FIG. 5 describes convergence state detection means of an optical discdrive according to a first embodiment of the present invention;

FIG. 6 describes convergence state detection means of an optical discdrive according to a third embodiment of the present invention;

FIG. 7 describes convergence state detection means of an optical discdrive according to a fourth embodiment of the present invention;

FIGS. 8A to 8D describe the configuration of an optical disc accordingto a first embodiment of the present invention;

FIG. 9 describes a waveform after signal quality improvement by anoptical disc drive according to a fourth embodiment of the presentinvention;

FIG. 10 is a graph used to describe an optical disc according to a firstembodiment of the present invention;

FIG. 11 is a graph used to describe an optical disc drive according to asixth embodiment of the present invention;

FIG. 12 is a graph used to describe an optical disc drive according to aseventh embodiment of the present invention;

FIG. 13 is a graph used to describe an optical disc drive according to aeighth embodiment of the present invention;

FIG. 14 is a graph used to describe an optical disc drive according to aninth embodiment of the present invention;

FIG. 15 is a graph used to describe an optical disc drive according to atenth embodiment of the present invention;

FIGS. 16A and 16B are graphs used to describe equalizer characteristicsin a seventh embodiment of the invention;

FIG. 17 is used to describe a focusing position in an eighth embodimentof the present invention;

FIG. 18 is used to describe a tracking position in a ninth embodiment ofthe present invention;

FIG. 19 is used to describe radial tilt in a tenth embodiment of thepresent invention;

FIG. 20 is used to describe a tangential tilt of an optical disc in asecond embodiment of the present invention;

FIG. 21 is used to describe convergence state detection means in anoptical disc drive according to a second embodiment of the presentinvention;

FIG. 22 describes the waveform after signal quality improvement by anoptical disc drive according to a fifth embodiment of the presentinvention;

FIG. 23 is used to describe signal recording and playback by an opticaldisc drive according to the prior art;

FIG. 24 is used to describe signal recording and playback by an opticaldisc drive according to the prior art;

FIG. 25 shows experimental results from recording and playback by anoptical disc drive according to the prior art;

FIG. 26 shows experimental results from recording and playback by anoptical disc drive according to an eleventh embodiment of the presentinvention;

FIG. 27 is a block diagram of an optical disc drive according to atwelfth embodiment of the present invention;

FIG. 28 is used to describe the recording compensation principle of atwelfth embodiment of the present invention;

FIG. 29 is used to describe the recording compensation principle of atwelfth embodiment of the present invention;

FIG. 30 shows the configuration of an optical disc according to aneleventh embodiment of the present invention;

FIG. 31 describes a thirteenth embodiment of the present invention;

FIG. 32 is a flow chart of the recording and playback process in athirteenth embodiment of the present invention;

FIG. 33 is a flow chart of the recording and playback process in afourteenth embodiment of the present invention;

FIG. 34 shows an optical disc recorded and reproduced by an optical discdrive according to a first embodiment of the present invention;

FIG. 35 shows the configuration of an optical disc according to thefifteenth and sixteenth embodiments of the present invention; and

FIG. 36 is used to describe the recording compensation principle of thefourteenth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention are described belowwith reference to the accompanying figures.

Embodiment 1

FIG. 1 is a block diagram of an optical disc drive according to a firstembodiment of the present invention. Shown in FIG. 1 are an optical disc101, semiconductor laser 102, collimator lens 103, beam splitter 104,convergent lens 105, collective lens 106, photodetector 107, playbacksignal operating means 108, focus controller 109, tracking controller110, actuator 111, convergence detector 112, laser drive unit 113, andsignal processing unit 115.

The playback operation of this optical disc drive is described next.

The optical disc 101 in this example has two data recording layers. Alight spot from the laser is converged on one of these two layers toread data from that layer.

The light beam emitted from the semiconductor laser 102 passes thecollimator lens 103, beam splitter 104, and convergent lens 105, and iscollected on one of the two data recording layers. The collected lightspot is reflected and diffracted by the optical disc 101, passes backthrough the convergent lens 105, beam splitter 104, and collective lens106, and is collected on the photodetector 107. Photodetection elementsA, B, C, D of the photodetector 107 each output a voltage signalcorresponding to the amount of light collected thereon, and the playbacksignal operating means 108 performs an arithmetic operation on thesevoltage signals.

The playback signal operating means 108 passes output signal FE to thefocus controller 109, output signal TE to the tracking controller 110,and output signal RF to the convergence detector 112.

The focus controller 109 applies voltage determined by output signal FEto the actuator 111 to control the focal position of the light spot onone of the two data recording layers of the optical disc 101.

The tracking controller 110 similarly applies voltage determined byoutput signal TE to the actuator 111 to control the tracking position ofthe light spot so that the spot tracks a desired track on the desireddata recording layer of the optical disc 101.

Information recorded to the optical disc is read by reading the prepitpeaks and valleys on the optical disc or by reading the marks and spaceswith different reflectance on a phase change optical disc.

The convergence detector 112 detects from the RF signal on which of thetwo data recording layers on the optical disc 101 the light spot isconverged. The result is passed to the laser drive unit 113, whichcontrols light output from the semiconductor laser 102.

The structure of the optical disc 101 is described next.

An example of the optical characteristics of an optical disc with twodata recording layers is described first with reference to FIG. 3.

The data recording layer on the side to which the laser beam is incidentis the first data layer. Only light beams that have passed through thefirst data layer reach the second data layer. An optical disc drive forphase change media drives a semiconductor laser at a peak power level toconvert crystalline spaces in the data layer to amorphous marks, or at abias power level to convert the amorphous marks to crystalline spaces.By emitting the laser to the optical disc at the appropriate powerlevel, the optical disc drive creates the marks (amorphous) and spaces(crystalline) used to encode data.

The structures of the first and second data layers are described next.

In the first data layer, the reflectance 301 of a crystalline space is9%, crystalline absorption 302 is 41%, and crystalline transmittance 303is 50%. Note that these percentages are based on the intensity of theemitted light beam being 100%.

The reflectance 304 of the amorphous marks in the first data layer is3%, amorphous absorption 305 is 27%, and amorphous transmittance 306 is70%.

A signal detected from the data area of the first layer corresponds to asignal for which the difference (ΔR1) between the first layercrystalline reflectance 301 and first layer amorphous reflectance 304 isdetected. This first layer ΔR1 is 6%.

In the second data layer, the reflectance 307 of a crystalline space is13%, crystalline absorption 308 is 65%, and crystalline transmittance309 is 22%.

The reflectance 310 of the amorphous marks in the second data layer is37%, amorphous absorption 311 is 37%, and amorphous transmittance 312 is26%.

A signal detected from the data area of the second layer corresponds toa signal for which the difference (ΔR2) between the second layercrystalline reflectance 307 and second layer amorphous reflectance 310is detected.

However, only light that has passed the first data layer reaches thesecond data layer. Likewise, only the light that is reflected anddiffracted by the second data layer and then passes back through thefirst data layer reaches the photodetector.

First layer transmittance differs in the crystalline spaces andamorphous marks, and as noted above is 50% in the crystalline parts and70% in the amorphous parts. When the disc is initialized, the entirefirst layer is crystalline. When the entire first layer is crystallineand first layer crystalline transmittance 303 is 50%, 50% of the emittedlight reaches the second layer. Of the light that is reflected anddiffracted by the second layer, only 50% passes back through the firstlayer. There is, therefore, a light loss of 25% (=50%*50%) as a resultof the light passing the first layer to the second layer passing backagain through the first layer. The second layer signal amplitude (ΔR2)is therefore the product of the 25% loss resulting from two passesthrough the first layer and the difference between the second layercrystalline reflectance and second layer amorphous reflectance. As aresult, ΔR2=−24%*25%=−6%. Note that the difference between thecrystalline reflectance and amorphous reflectance when calculating ΔR1and ΔR2 is obtained by simple subtraction, that is, (crystallinereflectance)−(amorphous reflectance). Note, further, that ΔR2 for thesecond layer is a negative value because the second layer crystallinereflectance is less than second layer amorphous reflectance.

Signal amplitude in the first layer data area and second layer data areacan be balanced by providing the above described optical characteristicsin an optical disc with two data layers, and stable, uniform signalquality can be assured in both the first and second layers.

The data recording and playback processes are described next below withreference to FIG. 4.

When an optical disc is inserted to the optical disc drive, the laserdrive unit 113 emits a laser beam in the laser drive step (laser on).The focus controller 109 then adjusts the focal position of the lightspot to a desired track in a desired data layer at a particular radialposition of the disc (focus on). The tracking controller 110 thencontrols the tracking position of the light spot to a particular trackin the first layer in the tracking control step (tracking on). Theconvergence detector 112 then detects which layer the light spot isconverged on in the convergence detection step (recording layerdetection).

What happens when the light spot is detected by the convergencedetection step to converge on the first layer is described next.

The laser drive step (laser power adjustment) is instructed to adjustlaser power so that the playback signal is optimized for the firstlayer. The laser drive step thus optimizes semiconductor laser power,and the address information is accurately detected (first layer addressdetection) based on the data output by the playback signal operatingstep (playback signal operating means 108). Data recording or playbackthen starts from a specified sector in the first layer.

What happens when the light spot is detected by the convergencedetection step to converge on the second layer is described next.

The laser drive step (laser power adjustment) is instructed to adjustlaser power so that the playback signal is optimized for the secondlayer. The laser drive step thus optimizes semiconductor laser power,and the address information is accurately detected (second layer addressdetection) based on the data output by the playback signal operatingstep (playback signal operating means 108). Data recording or playbackthen starts from a specified sector in the second layer.

The playback principle when reading an address area from an optical discwith optical characteristics as shown in FIG. 3 is described next.

FIG. 8A is a schematic diagram showing an address area and the firstlayer guide groove 801 of the optical disc. The guide groove 801 is agroove track. Groove tracks 801 are separated by land tracks 802. Theoptical disc is manufactured with the guide groove tracks 801 andprepits 805 formed at constant intervals on the disc as addressinformation indicating a specific location (address) on the disc. Theareas where the prepits are formed in the guide grooves of the opticaldisc are called address areas 806, and the other areas formed in theguide grooves where data is writable are called data areas. Addressinformation is expressed by the presence (or lack) of the prepits andvarying the length of the prepits in the address areas 806. The addressareas also contain an area where spaces and pits of the same length arepreformed. Reference numeral 803 indicates the repeated pit train in thefirst part of the address area (referred to below as the first pittrain), and reference numeral 804 indicates the repeated pit train inthe second part of the address area (referred to below as the second pittrain). These repeated pit trains in the first and second parts of theaddress area are staggered on the inside circumference and outsidecircumference sides of the guide groove track 801. The distance betweenthe groove track center and the center of the first pit train is Wa, andthe distance between the groove track center and the center of thesecond pit train is Wb. The distance between adjacent pit trains istrack pitch Tp. The relationship between Wa, Wb, and Tp is Wa=Wb=Tp/2.Reference numeral 807 indicates the prepit depth; the depth of prepitsin the first layer is d1, and the depth of prepits in the second layeris d2.

While the structure of the first layer is shown in FIG. 8A and describedabove, it will be noted that the structure of the second layer isidentical to the first layer except that the prepit depth in the secondlayer is d2.

The waveform of the playback signal when the light spot passes theaddress area as shown in FIG. 8A is shown in FIG. 5.

When the light spot scans the address area of the first layer isdescribed next.

The top part of FIG. 5 shows the playback signal waveform 501 from thefirst pit train in the first layer, and the playback signal waveform 502from the second pit train in the first layer. Reference numeral 503indicates the voltage from the ground level 504 of the average of themedians of the playback signal waveforms from the first pit train andthe second pit train. Reference numeral 505 is the maximum signalamplitude ΔAR1 from the first layer address area, and in an optical discwith optical characteristics as shown in FIG. 3 ΔAR1 is 3%.

When the light spot scans the address area of the second layer isdescribed next.

The bottom part of FIG. 5 shows the playback signal waveform 506 fromthe first pit train in the second layer, and the playback signalwaveform 507 from the second pit train in the second layer. Referencenumeral 508 indicates the voltage from the ground level 509 of theaverage of the medians of the playback signal waveforms from the firstpit train and the second pit train. Reference numeral 510 is the maximumsignal amplitude ΔAR2 from the second layer address area, and in anoptical disc with optical characteristics as shown in FIG. 3 ΔAR2 is1.1%.

The diffraction ratio of the prepits to the mirror surface area, whichis the amount of light diffracted by the pits and returning to thephotodetector, is 66%. Prepit depth is the same in the first and secondlayers. The prepit diffraction ratio to the mirror area depends upon theprepit depth, width, and length, and while is described as 66% in thisexample, the diffraction ratio can obviously differ. The differencebetween the maximum signal amplitude 505 from the first layer addressarea and the maximum signal amplitude 510 from the second layer addressarea is approximately three times, and the prepit addresses cannot becorrectly reproduced in each of the layers due to differences in thesignal quality from the first layer and second layer.

It is therefore necessary to determine whether the light spot isconverged on the first layer or second layer using the convergencedetector 112 shown in FIG. 1 to improve playback signal quality in theaddress area accordingly.

The prepit amplitude is changed in the first layer and second layer inorder to adjust the signal amplitude in the address areas of the firstand second layers.

The relationship between prepit depth and the playback signal amplitudeof the prepit address areas is shown in FIG. 10. As shown in FIG. 10,prepit address playback signal amplitude is greatest when the lightwavelength is λ if the effective prepit groove depth is λ/4.

The difference between the signal amplitude from address prepits in thefirst and second layers can be reduced in an optical disc according tothe present invention by adjusting prepit depth in the first layer andprepit depth in the second layer.

This is described more specifically below.

Second layer address amplitude can be increased by forming the prepitsas shown in FIG. 8B so that:d 1<d 2<=λ/4.

By making the depth of second layer prepits less than or equal to λ/4and approximately λ/4, and making the prepit depth in the first layerless than the prepit depth in the second layer to reduce the first layeraddress amplitude, a disc configured as described by the above equationhas the effect of increasing playback signal amplitude from the secondlayer address prepits, and improving signal amplitude in the secondlayer address area by reducing playback signal amplitude from the firstlayer address prepits and reducing the amplitude difference in signalsfrom the first layer and second layer address prepits.

Another possible configuration is shown in FIG. 8C, which can beexpressed as:d 1<λ/4<=d 2, and d 1>(d 2−λ/4).

In this configuration the groove depth of second layer prepits isgreater than or equal to λ/4 and approximately equal to λ/4, and thedepth of first layer prepits is less than (second layer prepit depth)minus (λ/4) to reduce first layer address amplitude, thereby increasingplayback signal amplitude from second layer address prepits. Inaddition, signal amplitude from second layer address areas is improvedby reducing playback signal amplitude from the first layer addressprepits and reducing the amplitude difference between playback signalsfrom first and second layer address prepits.

A yet further possible configuration is shown in FIG. 8D and can beexpressed as:λ/4<=d 2<d 1.

In this configuration the depth of second layer prepits is greater thanor equal to λ/4 and approximately equal to λ/4, and the first layerprepit depth is greater than the second layer prepit depth to reduce thefirst layer address signal amplitude, thereby effectively increasing theplayback signal amplitude from second layer address prepits. Inaddition, the second layer address area playback signal amplitude isimproved by reducing the playback signal amplitude from the first layeraddress prepits and reducing the amplitude difference between playbacksignals from first and second layer address prepits.

The depth of prepits in an optical disc according to the presentinvention refers to the optical depth or height with consideration forthe refractivity of the medium.

Embodiment 2

A method for discriminating the first layer and second layer of anoptical disc using a physical feature of the disc is described in theabove first embodiment using an optical disc in which the groove depthis different in the first and second layers. This second embodiment ofthe invention describes a method whereby the disc recorder or playerdiscriminates the first and second layers using an optical disc in whichthe groove depth is the same in the first and second layers.

The following second to fourth embodiments describe a convergencedetector 112 for determining whether the light spot is focused on thefirst layer or on the second layer when a signal is generated byfocusing a light spot on the optical disc.

A second embodiment of the invention is described first with referenceto the figures.

The convergence detector 112 for detecting light spot convergence usinga playback signal from the prepits in the address area is described withreference to FIG. 5 and FIG. 21. The configuration of the optical discdrive is identical to that of the first embodiment shown in FIG. 1.

In order to determine whether the light spot is focused on the firstlayer or second layer, the convergence detector 112 of the optical discdrive of the present invention determines the slice level voltage 2103of the address signal, which is the average of the median of theplayback signal waveform of the first pit train 2101 and the median ofthe playback signal waveform of the second pit train 2102, and thendetermines whether the slice level is in a first voltage range (betweenthreshold value 1 a and threshold value 1 b) or a second voltage range(between threshold values 2 a and 2 b). If the slice level voltage isbetween threshold values 1 a and 1 b, the address signal was read fromthe first layer; if between threshold values 2 a and 2 b, the addresssignal was read from the second layer.

The ranges of threshold values 1 a to 1 b and threshold values 2 a to 2b do not overlap. If, for example, as shown in FIG. 5, the slice levelis in the range(1 a−1 b)=7.5%±Δ,the address signal is from the first layer; if the slice level is in therange(2 a−2 b)=2.75%±Δ,the address signal is from the second layer. The convergence detector112 determines from which layer the signal is read. Note that Δ is 10%of the value on the left. The threshold value range 1 a to 1 b istherefore (7.5%+0.75%) to (7.5%−0.75%). The same denotation is usedbelow.

If there are three or more data recording layers, it is only necessaryto define additional constant slice level voltage ranges.

Alternatively, the convergence detector 112 in the optical disc drive ofthis invention can determine whether the light spot is focused on thefirst layer or second layer based on the maximum address amplitudevoltage 2105 detected from the address area. If the maximum addressamplitude is within a specified range (threshold values 1 c to 1 d), theaddress is read from the first layer; if within another specific range(threshold values 2 c to 2 d), the second layer is recognized.

The threshold value ranges 1 c to 1 d and 2 c and 2 d also do notoverlap. For example, referring again to FIG. 5, maximum address areaamplitude ΔAR1=(1 c−1 d)=3%±Δ and identifies the first layer; and

maximum address area amplitude ΔAR2=(2 c−2 d)=1.1%±Δ and identifies thesecond layer. The convergence detector 112 also makes thisdetermination.

If the number of plural data recording layers is 3 or more, it is againalso only necessary to define additional constant maximum address signalamplitude ranges.

This second embodiment of the invention can thus determine from theaddress area signal on which of plural data recording layers on theoptical disc the light spot is focused.

FIG. 21 shows an example for layer X on a disc with N data recordinglayers.

Embodiment 3

A third embodiment of the present invention is described next below withreference to the accompanying figures.

The convergence detector 112 in this third embodiment detects light spotconvergence using signals from unrecorded tracks in the data area, andis described with reference to FIG. 5 and FIG. 6. The configuration ofthe optical disc drive is identical to that of the first embodimentshown in FIG. 1.

In order to determine whether the light spot is focused on the firstlayer or second layer, the convergence detector 112 of the optical discdrive of the present invention holds the groove level 602, that is, theplayback signal level from an unrecorded track in the data area. Thelight spot is focused on the first layer if the groove level is in aspecific range (between threshold values 1 e and 1 f), and is focused onthe second layer if the groove level is in another specific range(between threshold values 2 e and 2 f).

If there are three or more data recording layers, it is only necessaryto define additional specific groove level voltage (threshold value)ranges. It will also be noted that threshold value range 1 e to 1 f andthreshold value range 2 e to 2 f do not overlap.

As shown in FIG. 5, for example, if the groove level is in the range(1 e−1 f)=6%±Δ,the light spot is focused on the first layer. If it is in the range(2 e−2 f)=2.2%±Δ,the light spot is focused on the second layer. The convergence detector112 makes this determination.

Alternatively, the convergence detector 112 in the optical disc drive ofthis invention can determine whether the light spot is focused on thefirst layer or second layer by holding the mirror level 601, which isthe playback signal level from the mirror area of the disc. As shown inFIG. 8A, the mirror area is the flat area between the groove track 801and the first pit train 803, and between the first pit train 803 andsecond pit train 804.

The light spot is focused on the first layer if the mirror level is inone specific voltage range (between threshold values 1 g and 1 h), andis focused on the second layer if the mirror level is in anotherspecific voltage range (between threshold values 2 g and 2 h).

Note that a mirror area is a mirror polished area of the disc whereneither guide grooves or prepits are formed.

If the number of plural data recording layers is 3 or more, it is againalso only necessary to define additional constant mirror level voltageranges. It will also be noted that threshold value ranges 1 g to 1 g and2 g to 2 h do not overlap.

As shown in FIG. 5, for example, if the mirror level is in the range(1 g−1 h)=9%±Δ,the light spot is focused on the first layer. If it is in the range(2 g−2 h)=3.3%±Δ,the light spot is focused on the second layer. The convergence detector112 makes this determination.

As described above, the present invention can identify the datarecording layer on which the light spot is focused in an optical dischaving plural data recording layers based on a signal from an unrecordedtrack in the data area.

Embodiment 4

A fourth embodiment of the present invention is described next belowwith reference to the accompanying figures.

The convergence detector 112 in this fourth embodiment detects lightspot convergence using signals from recorded tracks in the data area,and is described with reference to FIG. 7. The configuration of theoptical disc drive is identical to that of the first embodiment shown inFIG. 1.

In FIG. 7 reference numerals 701 to 706 show the playback signalwaveform from the mirror area and recording signal area (part of groovetrack 801 in FIG. 8) of the first layer, and reference numerals 707 to712 show the playback signal waveform from the mirror area and recordingsignal area (part of groove track 801 in FIG. 8) of the second layer.Note that the recording signal envelope in the first layer is below thegroove level 704. As will be clear from FIG. 3, this is because when amark is written in the first layer (changing the phase change film ofthe disc from a crystalline to amorphous state), the reflectance dropsfrom 9% to 3%. In the second layer, however, the recording signalenvelope is above the groove level 710. This will also be clear fromFIG. 3 because when a mark is written to the second layer, reflectancerises from 13% to 37%. This is because the composition of the phasechange layer is different in the first and second layers.

How the convergence detector 112 in the optical disc drive of thisembodiment determines whether the light spot is focused on the firstlayer or second layer is described below. How the convergence detector112 determines that the light spot is focused on the first layer whenthe light spot is focused on the first layer is described first.

The convergence detector 112 holds the mirror-slice level voltagedifference 702, which is the voltage difference between the recordingsignal slice level 703 (the median of the signal amplitude of therecording signal envelope, that is, the waveform of the playback signalfrom the data area recording track being read) and the voltage of themirror level 701 signal (that is, a signal read from a flat mirrorsurface area where no guide grooves or prepits are formed).

If the mirror-slice level voltage difference 702 is in a specific range(between threshold values 1 i and 1 j), the light spot is focused on thefirst layer.

How the convergence detector 112 determines that the light spot isfocused on the second layer when the light spot is focused on the secondlayer is described first.

The convergence detector 112 holds the mirror-slice level voltagedifference 708, which is the voltage difference between the recordingsignal slice level 709 (the median of the signal amplitude of therecording signal envelope, that is, the waveform of the playback signalfrom the data area recording track being read) and the voltage of themirror level 707 signal (that is, a signal read from a flat mirrorsurface area where there are no guide grooves or prepits).

If the mirror-slice level voltage difference 708 is in a specific range(between threshold values 2 i and 2 j), the light spot is focused on thesecond layer.

As in the previous embodiments, ranges 1 i to 1 j and 2 i to 2 j do notoverlap.

As shown in FIG. 7, for example, if the mirror-slice level voltagedifference is in the range(1 i−1 j)=4.95%±Δ,the light spot is focused on the first layer. If it is in the range(2 i−2 j)=1%±Δ,the light spot is focused on the second layer. The convergence detector112 makes this determination.

The maximum recording signal level, which is the highest recordingsignal level, can be used in place of the recording signal slice level.Further alternatively, the minimum recording signal level, which is thelowest recording signal level, can also be used in place of therecording signal slice level.

If the number of plural data recording layers is 3 or more, it is alsoonly necessary to define additional constant mirror-slice level voltagedifference ranges.

Alternatively, the convergence detector 112 in the optical disc drive ofthis invention can determine whether the light spot is focused on thefirst layer or second layer by holding the groove-slice voltagedifference 706, which is the voltage difference between the recordingsignal slice level 703 (the median of the signal amplitude of therecording signal envelope, that is, the waveform of the playback signalfrom the data area recording track being read) and the groove level 704voltage, that is, a signal read from an unrecorded guide groove. If thedifference of the (recording signal slice level)−(groove level) ispositive, the light spot is focused on the first layer; if negative, thelight spot is focused on the second layer.

Depending upon the optical disc, the light spot may be focused on thefirst layer when the (recording signal slice level)−(groove level)difference is negative, and focused on the second layer when thedifference is positive.

It will thus be known that the present invention can also determine fromsignals read from recorded tracks in the data area on which of pluraldata recording layers the light spot is focused.

Embodiment 5

A fifth embodiment of the present invention is described next below withreference to the accompanying figures. The second to fourth embodimentsabove describe a convergence detector 112 for discriminating between thefirst and second layers of an optical disc. The fifth to seventhembodiments below describe how to make signal output from the secondlayer identical to signal output from the first layer when theconvergence detector 112 determines that the light spot is focused onthe second layer.

This is described first with reference to FIG. 1.

The laser drive unit 113 is controlled to drive the semiconductor laser102 at an output level optimized for the first layer when theconvergence detector 112 determines that the light spot is focused onthe first layer or it is not clear which layer the light spot is focusedon.

If the convergence detector 112 determines that the light spot isfocused on the second layer, the convergence detector 112 controls thelaser drive unit 113 to drive the semiconductor laser 102 at an outputlevel optimized for the second layer. In this case the laser drive unit113 drives the semiconductor laser 102 at approximately 2.7 times theoutput power when the light spot is focused on the first layer. Why avalue of 2.7 times is used is described below.

Scanning the address area with the light spot is described withreference to FIG. 9, referring specifically to scanning an address areain the first layer.

Reference numeral 901 is the playback signal waveform of the first pittrain in the first layer, and reference numeral 902 is the playbacksignal waveform of the second pit train in the first layer. Referencenumeral 903 indicates the maximum signal amplitude ΔAR1 of the firstlayer address area, which in an optical disc with opticalcharacteristics as shown in FIG. 3 is 3%. Reference numeral 904indicates the ground level voltage. The maximum signal amplitude 505 ofthe first layer address area is also shown as ΔAR1=3% in FIG. 5.

Scanning the address area of the second layer with a light spot emittedat the same laser power level used for the first layer instead ofdriving the laser drive unit 113 at 2.7 times the first layer powerlevel is described next. Note that the maximum amplitude ΔAR2 of thesecond layer address area is 1.1%, as also shown in FIG. 5 as themaximum signal amplitude 510 of the second layer address area. However,by multiplying laser power 2.7 times, the maximum amplitude ΔAR2 of 1.1%can be increased to 3%. Therefore, when the convergence detector 112shown in FIG. 1 according to this fifth embodiment determines that thelight spot is focused on the second layer, the laser drive unit 113drives the laser to output a light spot at 2.7 times the power levelused when the light spot is focused on the first layer.

Reference numeral 905 in FIG. 9 shows the playback signal waveform ofthe first pit train in the second layer when the light spot is emittedat 2.7 times the first layer power level, and reference numeral 906shows the playback signal waveform of the second pit train from thesecond layer. Reference numeral 907 shows the maximum signal amplitudeof the second layer address area. When the convergence detector 112detects that the light spot is focused on the second layer, the laserdriver drives the semiconductor laser at 2.7 times the output level forthe first layer, and the amount of light incident on the photodetectoris therefore 2.7 times the light output of the first layer. The maximumsignal amplitude ΔAR2 of the second layer address area is therefore 3%.

The maximum signal amplitude of the address area is therefore 3% in boththe first and second layers, and playback signal quality is thereforeimproved in the first and second layer address areas.

It should be noted that while semiconductor laser output is increased2.7 times when the light spot is focused on the second layer comparedwith when focused on the first layer, this increase is determined by thefirst layer crystalline reflectance, the second layer crystallinereflectance, and the first layer absorption.

This increase is also determined by the state of the recorded andunrecorded tracks of the first layer directly below the second layer.

It is further possible to restrict increase laser output 2.7 times towhen the light spot is focused on the address areas of the second layer.

Yet further, the increase in laser output can be different in the dataareas and address areas of the second layer.

Embodiment 6

A sixth embodiment of the present invention is described next below withreference to FIG. 11.

Shown in FIG. 11 are an optical disc 1101, semiconductor laser 1102,collimator lens 1103, beam splitter 1104, convergent lens 1105,collective lens 1106, photodetector 1107, playback signal operatingmeans 1108, focus controller 1109, tracking controller 1110, actuator1111, convergence detector 1112, laser drive unit 1113, gain controller1114, and signal processing unit 1115.

When the light spot is focused on the first layer or the focal point isundetermined, the convergence detector 1112 controls the gain controller1114 so that the gain in the output voltage of the photodetector isoptimized for the first layer.

When the light spot is focused on the second layer, the convergencedetector 1112 controls the gain controller 1114 so that the gain in theoutput voltage of the photodetector is optimized for the second layer.In this case the convergence detector 1112 instructs the gain controller1114 to set the gain in the output voltage of the photodetector 1107 to2.7 times the gain when the light spot is focused on the first layer.Why 2.7 times the gain is used is as described in the fifth embodimentabove.

The light spot scanning an address area in the first layer is describednext.

Reference numeral 901 is the playback signal waveform of the first pittrain in the first layer, and reference numeral 902 is the playbacksignal waveform of the second pit train in the first layer. Referencenumeral 903 indicates the maximum signal amplitude ΔAR1 of the firstlayer address area, which in an optical disc with opticalcharacteristics as shown in FIG. 3 is 3%. Reference numeral 904indicates the ground level voltage.

The light spot scanning an address area in the second layer is describednext.

FIG. 9 shows scanning the second layer at 2.7 times the light spot poweremitted to the first layer. Reference numeral 905 shows the playbacksignal waveform of the first pit train in the second layer, andreference numeral 906 shows the playback signal waveform of the secondpit train from the second layer. Reference numeral 907 shows the maximumsignal amplitude of the second layer address area. When the convergencedetector detects that the light spot is focused on the second layer, thelaser driver is controlled so that the output voltage gain of thephotodetector 1107 is 2.7 times the first layer gain, and the outputvoltage of the photodetector is therefore 2.7 times the output voltagewhen reading the first layer. The maximum signal amplitude ΔAR2 of thesecond layer address area is therefore 3%.

The maximum signal amplitude is therefore 3% for signals read from theaddress areas of the first and second layers, and playback signalquality is therefore improved in the address areas of both the first andsecond layers.

It should be noted that the gain controller sets the output voltage gainof the photodetector when the light spot is focused on the second layerto 2.7 times the gain when the light spot is focused on the first layer,but this gain rate is determined by the first layer crystallinereflectance, the second layer crystalline reflectance, and the firstlayer absorption.

This gain rate is also determined by the state of the recorded andunrecorded tracks of the first layer directly below the second layer.

It is further possible to restrict increase the gain in photodetectoroutput to 2.7 times to when the light spot is focused on the addressareas of the second layer.

Yet further, the increase in photodetector gain can be different in thedata areas and address areas of the second layer.

Embodiment 7

A seventh embodiment of the present invention is described next belowwith reference to FIG. 12.

Shown in FIG. 12 are optical disc 1201, semiconductor laser 1202,collimator lens 1203, beam splitter 1204, convergent lens 1205,collective lens 1206, photodetector 1207, playback signal operatingmeans 1208, focus controller 1209, tracking controller 1210, actuator1211, convergence detector 1212, laser drive unit 1213, equalizationcontroller 1214, and signal processing unit 1215. The equalizationcontroller is a device that can selectively increase the gain of aspecific frequency component.

The output of the convergence detector 1212 is obtained by a method usedby the convergence detector in the second, third, or fourth embodiment.

When the light spot is focused on the first layer or the focal point isundetermined, the convergence detector 1212 controls the equalizationcontroller 1214 so that the output voltage of the playback signaloperating means 1208 is equalized with equalization characteristicsoptimized for the first layer.

When the light spot is focused on the second layer, the convergencedetector 1212 controls the equalization controller 1214 so that theoutput voltage of the playback signal operating means 1208 is equalizedwith equalization characteristics optimized for the second layer.

As shown in FIG. 16A, for example, the equalization controller 1214 ispreset with two equalization curves. The first curve is set to achievethe greatest gain at frequency 1/2T and gain G1, and the other curve isset to achieve the greatest gain at frequency 1/2T and gain G2 whereG1<G2. If the convergence detector 1212 detects that the light spot isfocused on the first layer, one equalization curve is selected, and ifthe light spot is focused on the second layer, the other equalizationcurve is selected.

The equalization curves can alternatively be set as shown in FIG. 16B sothat the greatest gain is achieved at frequency 1/2T and gain G1 on onecurve, and at frequency 1/3T and gain G1 on the other curve.

It is also possible to tune the equalization characteristics afterselecting the equalization curve. In this case the equalizationcontroller 1214 outputs to the signal processing unit 1215, and thesignal processing unit 1215 outputs the playback signal, but theequalization controller 1214 is then tuned based on jitter detected inthe playback signal from the signal processing unit 1215. Tuning couldalso be based on the byte error rate (BER), resolution, or asymmetryinstead of jitter.

The equalization characteristics for each layer are tuned by comparingthe index (such as jitter, BER, resolution, asymmetry) of playbacksignal quality with a specific threshold value.

Jitter is a time shift from the playback signal of the original signal,and if the recording conditions are equal, low jitter generallyindicates that playback is more accurate. Therefore, if jitter is lessthan or equal to a specific threshold value, best equalizationcharacteristic has been achieved.

The BER indicates the error rate in the playback signal, and a low BERgenerally indicates accurate playback. Therefore, if the BER is lessthan or equal to a specific threshold value, the best equalizationcharacteristic has been achieved.

Resolution is the ratio between the amplitude of the signal with theshortest or proportionately shortest time interval in the playbacksignal, and the amplitude of the signal with the longest orproportionately longest time interval in the playback signal, and if therecording conditions are equal, high resolution generally indicates thatplayback is more accurate. Therefore, if resolution is greater than orequal to a specific threshold value, the best equalizationcharacteristic has been achieved.

Asymmetry is a value indicative of the second harmonic component of theplayback signal, and if the recording conditions are equal, lowerasymmetry generally indicates that playback is more accurate. Therefore,if asymmetry is less than or equal to a specific threshold value, thebest equalization characteristic has been achieved.

It will also be obvious that while jitter, byte error rate, resolution,and asymmetry are used as indices of playback signal quality above,other indices may also be used, including signal amplitude, C/N, and thebit error rate.

It should also be noted that different equalization characteristics canbe set for the data areas and address areas of the same data recordinglayer.

The seventh embodiment of the invention as described above can thusimprove playback signal characteristics in the address areas or dataareas in each data recording layer, and can significantly improve thequality of playback signals from the address areas and data areas of theoptical disc.

Embodiment 8

An eighth embodiment of the present invention is described next belowwith reference to FIG. 13. Shown in FIG. 13 are optical disc 1301,semiconductor laser 1302, collimator lens 1303, beam splitter 1304,convergent lens 1305, collective lens 1306, photodetector 1307, playbacksignal operating means 1308, focus controller 1309, tracking controller1310, actuator 1311, convergence detector 1312, laser drive unit 1313,and signal processing unit 1315.

The output of the convergence detector 1312 is obtained by a method usedby the convergence detector in the second, third, or fourth embodiment.

When the light spot is focused on the first layer or the focal point isundetermined, the convergence detector 1312 controls the focuscontroller 1309 to optimize the focal point of the light spot on thefirst layer.

When the light spot is focused on the second layer, the convergencedetector 1312 controls the focus controller 1309 to optimize the focalpoint of the light spot on the second layer.

When the beam profile is seen in section as shown in FIG. 17, the focalpoint is optimized when the narrowest part of the beam (the beam waist)is perpendicular to, or perpendicularly intersects, the data recordinglayer of the optical disc. After thus selecting the focal point, thefocal point can be further tuned. The playback signal operating means1308 outputs to the signal processing unit 1315, which in turn outputsthe playback signal. The focal point can be tuned by detecting jitter inthe playback signal and then adjusting the focus controller 1309 basedon the detected jitter. Tuning could also be based on the byte errorrate (BER), resolution, or asymmetry instead of jitter.

The focal point for each layer can be tuned by comparing the index (suchas jitter, BER, resolution, asymmetry) of playback signal quality with aspecific threshold value.

Jitter is a time shift from the playback signal of the original signal,and if the recording conditions are equal, low jitter generallyindicates that playback is more accurate. Therefore, if jitter is lessthan or equal to a specific threshold value, the best focal point hasbeen achieved.

The BER indicates the error rate in the playback signal, and a low BERgenerally indicates accurate playback. Therefore, if the BER is lessthan or equal to a specific threshold value, the best focal point hasbeen achieved.

Resolution is the ratio between the amplitude of the signal with theshortest or proportionately shortest time interval in the playbacksignal, and the amplitude of the signal with the longest orproportionately longest time interval in the playback signal, and if therecording conditions are equal, high resolution generally indicates thatplayback is more accurate. Therefore, if resolution is greater than orequal to a specific threshold value, the best focal point has beenachieved.

Asymmetry is a value indicative of the second harmonic component of theplayback signal, and if the recording conditions are equal, lowerasymmetry generally indicates that playback is more accurate. Therefore,if asymmetry is less than or equal to a specific threshold value, thebest focal point has been achieved.

It will also be obvious that while jitter, byte error rate, resolution,and asymmetry are used as indices of playback signal quality above,other indices may also be used, including signal amplitude, C/N, and thebit error rate.

It should also be noted that different focal points can be set for thedata areas and address areas of the same data recording layer.

This embodiment of the invention as described above can thus improveplayback signal characteristics in the address areas or data areas ineach data recording layer, and can significantly improve the quality ofplayback signals from the address areas and data areas of the opticaldisc.

Embodiment 9

A ninth embodiment of the present invention is described next below withreference to FIG. 14.

Shown in FIG. 14 are optical disc 1401, semiconductor laser 1402,collimator lens 1403, beam splitter 1404, convergent lens 1405,collective lens 1406, photodetector 1407, playback signal operatingmeans 1408, focus controller 1409, tracking controller 1410, actuator1411, convergence detector 1412, laser drive unit 1414, and signalprocessing unit 1415.

The output of the convergence detector 1412 is obtained by a method usedby the convergence detector in the second, third, or fourth embodiment.

When the light spot is focused on the first layer or the focal point isundetermined, the convergence detector 1412 controls the trackingcontroller 1410 to optimize the tracking position of the light spot onthe first layer.

When the light spot is focused on the second layer, the convergencedetector 1412 controls the tracking controller 1410 to optimize thetracking position of the light spot on the second layer.

When the beam profile is seen in section as shown in FIG. 18, thetracking position refers to the location of the narrowest part of thebeam (the beam waist) relative to the track in the direction crossingthe track radially to the optical disc. After thus selecting thetracking position, the tracking position can be further tuned. Theplayback signal operating means 1408 outputs to the signal processingunit 1415, which in turn outputs the playback signal. The trackingposition can be tuned by detecting jitter in the playback signal andthen adjusting the tracking controller 1410 based on the detectedjitter. Tuning could also be based on the byte error rate (BER),resolution, or asymmetry instead of jitter.

The tracking position for each layer can be tuned by comparing the index(such as jitter, BER, resolution, asymmetry) of playback signal qualitywith a specific threshold value.

Jitter is a time shift from the playback signal of the original signal,and if the recording conditions are equal, low jitter generallyindicates that playback is more accurate. Therefore, if jitter is lessthan or equal to a specific threshold value, the best tracking positionhas been achieved.

The BER indicates the error rate in the playback signal, and a low BERgenerally indicates accurate playback. Therefore, if the BER is lessthan or equal to a specific threshold value, the best tracking positionhas been achieved.

Resolution is the ratio between the amplitude of the signal with theshortest or proportionately shortest time interval in the playbacksignal, and the amplitude of the signal with the longest orproportionately longest time interval in the playback signal, and if therecording conditions are equal, high resolution generally indicates thatplayback is more accurate. Therefore, if resolution is greater than orequal to a specific threshold value, the best tracking position has beenachieved.

Asymmetry is a value indicative of the second harmonic component of theplayback signal, and if the recording conditions are equal, lowerasymmetry generally indicates that playback is more accurate. Therefore,if asymmetry is less than or equal to a specific threshold value, thebest tracking position has been achieved.

It will also be obvious that while jitter, byte error rate, resolution,and asymmetry are used as indices of playback signal quality above,other indices may also be used, including signal amplitude, C/N, and thebit error rate.

It should also be noted that different tracking positions can be set forthe data areas and address areas of the same data recording layer.

This embodiment of the invention as described above can thus improveplayback signal characteristics in the address areas or data areas ineach data recording layer, and can significantly improve the quality ofplayback signals from the address areas and data areas of the opticaldisc.

Embodiment 10

A tenth embodiment of the present invention is described next below withreference to FIG. 15. Shown in FIG. 15 are optical disc 1501,semiconductor laser 1502, collimator lens 1503, beam splitter 1504,convergent lens 1505, collective lens 1506, photodetector 1507, playbacksignal operating means 1508, focus controller 1509, tracking controller1510, actuator 1511, convergence detector 1512, laser drive unit 1513,tilt controller 1515, and signal processing unit 1516.

The output of the convergence detector 1512 is obtained by a method usedby the convergence detector in the second, third, or fourth embodiment.

When the light spot is focused on the first layer or the focal point isundetermined, the convergence detector 1512 controls the tilt controller1515 to optimize the tilt position of the light spot for the firstlayer.

When the light spot is focused on the second layer, the convergencedetector 1512 controls the tilt controller 1515 to optimize the tiltposition of the light spot for the second layer.

The tilt position refers to the angle between the optical axis of thelaser beam and the data recording layer of the optical disc. After thusselecting the tilt position, the tilt position can be further tuned. Theplayback signal operating means 1508 outputs to the signal processingunit 1516, which in turn outputs the playback signal. The trackingposition can be tuned by detecting jitter in the playback signal andthen adjusting the tilt controller 1515 based on the detected jitter.Tuning could also be based on the byte error rate (BER), resolution, orasymmetry instead of jitter.

There are two types of tilt: radial tilt (R tilt) and tangential tilt (Ttilt). Radial tilt is tilt in the direction orthogonal to the track andradial to the disc. Tangential tilt is tilt in the direction parallel ortangential to the track.

Radial tilt is further described with reference to FIG. 19 in which areshown optical disc 1901, optical head 1902, and tilt stand 1903. Thereare two types of radial tilt: disc R tilt 1904 resulting from discwarping and fluctuations in the data surface due to disc rotation, anddrive R tilt 1905. Drive R tilt 1905 results from optical head mountingerror or biasing of the tilt stand causing the recording surface of theoptical disc 1901 to be tilted relative to the optical axis of the lightbeam. There is no practical need to differentiate between disc R tiltand drive R tilt, and both are collectively referred to as R tilt.

Tangential tilt (T tilt) is further described with reference to FIG. 20in which are shown optical disc 2001, optical head 2002, and tilt stand2003. There are also two types of tangential tilt, disc T tilt 2004 anddrive T tilt 2005. Disc T tilt 2004 results from disc rotationvibrations and error in the disc surface precision. Drive T tilt 2005results from optical head mounting error or biasing of the tilt standcausing the recording surface of the optical disc 2001 to be tiltedrelative to the optical axis of the light beam. There is no practicalneed to differentiate between disc T tilt and drive T tilt, and both arecollectively referred to as T tilt.

The R and T tilt positions for each layer can be tuned by comparing theindex (such as jitter, BER, resolution, asymmetry) of playback signalquality with a specific threshold value.

Jitter is a time shift from the playback signal of the original signal,and if the recording conditions are equal, low jitter generallyindicates that playback is more accurate. Therefore, if jitter is lessthan or equal to a specific threshold value, the best R and T tiltpositions have been achieved.

The BER indicates the error rate in the playback signal, and a low BERgenerally indicates accurate playback. Therefore, if the BER is lessthan or equal to a specific threshold value, the best R and T tiltpositions have been achieved.

Resolution is the ratio between the amplitude of the signal with theshortest or proportionately shortest time interval in the playbacksignal, and the amplitude of the signal with the longest orproportionately longest time interval in the playback signal, and if therecording conditions are equal, high resolution generally indicates thatplayback is more accurate. Therefore, if resolution is greater than orequal to a specific threshold value, the best R and T tilt positionshave been achieved.

Asymmetry is a value indicative of the second harmonic component of theplayback signal, and if the recording conditions are equal, lowerasymmetry generally indicates that playback is more accurate. Therefore,for determining whether or not the optimum tracking position isobtained, if asymmetry is less than or equal to a specific thresholdvalue, it is so determined that the best R and T tilt positions havebeen achieved.

It will also be obvious that while jitter, byte error rate, resolution,and asymmetry are used as indices of playback signal quality above,other indices may also be used, including signal amplitude, C/N, and thebit error rate.

This embodiment of the invention as described above can thus improveplayback signal characteristics in the address areas or data areas ineach data recording layer, and can significantly improve the quality ofplayback signals from the address areas and data areas of the opticaldisc.

As will be known from the preceding descriptions of an optical disc,optical disc drive, and optical disc playback method according to thepresent invention, which of plural data recording layers the light spotis focused on in an optical disc having a plurality of data recordinglayers can be determined irrespective of whether the data area isrecorded or blank. Playback signal quality in the address areas and dataareas can therefore be improved in each of the plural data recordinglayers, and it is therefore possible to significantly improve signalquality when reading from both the address areas and data areas of theoptical disc.

Embodiment 11

The recording principle of a phase change optical disc is described nextwith reference to FIG. 23.

A disc recorder for phase change media records and erases data byemitting a laser beam to a recording thin film of the disc in order toheat the phase change material of the thin film and thereby effect achange in the crystalline phase of the film. The y-axis in FIG. 23 showslaser power, and the x-axis shows the time base or a location on therotating disc. The semiconductor laser is primarily driven at a peakpower 2302 level causing crystalline parts to change to an amorphousstate, or a bias power 2303 level causing amorphous parts to change to acrystalline state. By emitting the semiconductor laser to the recordinglayer of the disc while modulating laser power between peak power 2302and bias power 2303, an appropriate sequence of recording marks(amorphous parts) 2304 and spaces 2305 (crystalline parts) between themarks 2304 is formed on the optical disc. As described above,reflectance differs in the recorded marks and spaces. This difference inmark and space reflectance is detected from the light spot focused onthe optical disc, and processed to read information.

Heat interference between adjacent recording marks in conjunction withhigh density recording can cause recorded mark length to shift from thenormal position in the recording signal. This problem is addressed byvarious adaptive recording compensation technologies, one of which isdescribed with reference to FIG. 24.

In FIG. 24 reference numeral 2401 shows a case in which the previousspace is short, and reference numeral 2402 shows a case in which theprevious space is long. If the previous space is short and data isrecorded with a normal recording signal 2407, heat interference causesthe leading edge of the recorded mark to shift +S3 2403 from the normalmark edge position, resulting in a longer mark. To compensate for thisthe position of the first pulse in the recording pulse train is delayed−S3 2405 so that the mark is recorded to the normal position afterrecording compensation 2408.

Similarly when the previous space is long and data is recorded with anormal recording signal 2407, heat interference causes the leading edgeof the recorded mark to shift −S6 2404 from the normal mark edgeposition, resulting in a shorter mark. To compensate for this theposition of the first pulse in the recording pulse train is advanced +S62406 so that the mark is recorded to the normal position after recordingcompensation 2408.

These recording compensation techniques thus suppress interferenceduring playback between marks and spaces of different lengths, and makeit possible to improve signal quality.

FIG. 25 is an eye pattern of the recording signal when this recordingcompensation technique is used. It will be known from the figure that aclear eye is opened by applying this adaptive recording compensationtechnique. Land and groove recording technologies record marks andspaces to both the land and groove tracks of the guide grooves on thedisc.

Problems associated with the prior art technologies noted above aredescribed below. Conventional double-sided optical recording media aredesigned such that recorded data is read and data is recorded to thedisc by emitting laser beams to the disc from both above and below thedisc. There is therefore little space for printing a label identifyingthe recorded content (disc), and handling the discs is thus difficult.Furthermore, if double-sided media is played in a drive with only oneoptical head, the disc must be removed from the drive, turned over, andreloaded in order to play the other side, and continuous, uninterruptedplayback of all recorded content is therefore not possible. To automatereading both sides of the disc it is necessary to provide two opticalheads, one on each side of the disc. This increases disc player size andcost.

The recording and playback characteristics of signals recorded to anoptical disc having optical characteristics as shown in FIG. 3 aredescribed next. FIG. 26 is a graph of test measurements taken with asample optical disc produced with the optical characteristics shown inFIG. 3. FIG. 26 shows peak power used to change the phase changematerial from crystalline to amorphous state on the x-axis, and the C/Nratio of the playback signal on the y-axis.

A phase change recording film was formed on two 0.58 mm thicksubstrates, which were then bonded with a 0.04 mm thick adhesive layertherebetween to form the optical disc. Laser power was changed whilerecording to each recording layer to form recording marks. The recordingmarks were then reproduced, and the C/N ratio of the playback signalmeasured. The results are shown in FIG. 26.

Curve 2601 shows the C/N ratio when data recorded to the first recordinglayer was reproduced. Curve 2602 shows the C/N ratio when data recordedto the second recording layer was reproduced.

When recording data to disc, disc surface wobble and eccentricity, andexternal impact or vibration on the recorder, cause defocusing andtracking error, thus resulting in a degraded C/N ratio in the recordingsignal. Tilt, that is, deviation in the angle between the disc andoptical axis of the light beam, also degrades the C/N ratio of therecording signal. Disc warping is also affected by humidity and otherenvironmental factors. The optical head is also affected by variationsresulting from the manufacturing process as well as aging. ConsideringC/N ratio degradation resulting from these and other factors, 45 dB isthe practical limit for the C/N ratio of the recording signal if datarecorded to disc is to be recorded and reproduced reliably.

The following conclusions can be drawn from FIG. 26. A C/N ratio of 45dB or more is achieved on the first data recording layer at a peak powerof 12 mW or greater, and is achieved on the second data recording layerwith a peak power of 13 mW or more. This shows that recordingsensitivity is different on the first and second data recording layers.

FIG. 26 also indicates that increasing the peak power should increasethe C/N ratio for both recording layers.

However, increasing the peak power of the laser shortens the servicelife of the laser, increases power consumption, and increasesaccumulation of recording film damage in the recording film throughrepeated recording. It is therefore desirable to set the recording poweras low as possible.

Therefore, to avoid these problems and assure good signal quality ineach recording layer, the peak power level of the recording laser mustbe set separately for the first recording layer and the second recordinglayer.

Determining the peak power is described next. The peak power can bedetermined by recording a signal containing a repeated sequence of theshortest marks and spaces in the recording data, and measuring the C/Nratio of the recorded signal.

For example, the peak power is set to the peak power achieving a C/Nratio of 50 dB in the recorded signal. The desirable peak powerachieving this C/N ratio is learned for both the first and secondrecording layers.

Instead of using the C/N ratio, peak power could alternatively be set bymeasuring jitter in the recording signal. In this case the peak power isdetermined by measuring jitter in a recorded signal containing arandomized pattern of marks and spaces.

The peak power settings learned for each of the recording layers arethen stored. When data is actually recorded, the convergence detectordetermines whether data is being written to the first recording layer orsecond recording layer, and the laser is then driven at the peak powersetting appropriate to the detected recording layer. The semiconductorlaser can thus be driven at an output level strong enough to assure goodsignal quality.

The present invention thus provides an optical disc drive that canrecord and reproduce optical recording media having two recording layersso that labels can be easily printed on the recording media, therecording media can be automatically recorded and reproduced using asingle optical head, and the recording media maintains goodcompatibility with optical recording media having only one recordinglayer.

It will be further noted that this optical disc drive and opticalrecording medium are designed so that the second recording layer isrecorded and read through the first recording layer.

The amount of light reaching the second layer differs when the firstlayer is recorded (thus containing a combination of crystalline spacesand amorphous marks) and when the first layer is blank (only crystallinephase). If when recording the second layer, for example, the phase ofthe first layer directly below (that is, between the laser and secondlayer) where the second layer is recorded is blank (that is, onlycrystalline phase), the first layer transmittance is 50% as shown inFIG. 3. However, if the intervening first layer is partially orcompletely recorded, transmittance increases in accordance with the areaof the recorded tracks in the first layer through which the light spotpasses to reach the second layer.

This eleventh embodiment of the present invention is further describedbelow with reference to FIG. 30. FIG. 30 shows the configuration of anoptical disc 1701 according to the present embodiment.

Shown in FIG. 30 are the read-only area 3002 disposed to the insidecircumference of the optical disc 3001, prepits 3004 preformed in theread-only area 3002, and the prepit track pitch 3005. The recordablearea 3003 is provided on the outside circumference side of the read-onlyarea 3002. Inside the recordable area 3003 are groove tracks 3005 andland tracks 3006, which are the tracks between the groove tracks.Reference numeral 3007 shows a mark formed in a groove track.

Information indicating which of the plural recording layers the lightspot is focused on is modulated and recorded to the prepits in theread-only area 3002. Both the recordable area 3003 and read-only area3002 are formed in each of the plural recording layers.

As a result, the convergence detector can identify which of the pluralrecording layers the light spot is focused on.

Embodiment 12

A twelfth embodiment of the present invention is described next belowwith reference to FIG. 27.

Shown in FIG. 27 are optical disc 2701, semiconductor laser 2702,collimator lens 2703, beam splitter 2704, convergent lens 2705,collective lens 2706, photodetector 2707, playback signal operatingmeans 2708, focus controller 2709, tracking controller 2710, actuator2711, convergence detector 2712, laser drive unit 2713, recordingcontroller 2715, and signal processing unit 2717.

The output of the convergence detector 2712 is obtained by a method usedby the convergence detector in the second, third, or fourth embodiment.

When the light spot is focused on the first layer or the focal point isundetermined, the convergence detector 2712 controls the recordingcontroller 2715 to set a recording compensation value optimized for thefirst layer.

When the light spot is focused on the second layer, the convergencedetector 2712 controls the recording controller 2715 to set a recordingcompensation value optimized for the second layer.

A method for setting an optimized recording compensation value isdescribed next with reference to FIG. 28 and FIG. 29. In FIG. 29reference numeral 2901 shows a NRZI signal. Reference numeral 2902 showsthe recording marks and spaces recorded for the NRZI signal 2901 beforerecording compensation. Note that the edges of the recording marks andspaces 2902 are offset from the reference edges of the NRZI signal dueto the effects of heat interference. To eliminate this edge shifting,the positions of the first pulse and last pulse in the recording pulsetrain are adjusted according to the recording mark length, and thelength of the spaces before and after the recording mark.

FIG. 28 shows examples of recording compensation tables. First pulseposition Tsfp 2801 indicates the position of the first pulse and isdetermined by the recording mark length and length of the precedingspace. For example, if the recording mark length is 3T and the length ofthe previous space is 3T, Tsfp is “a.” End pulse position Telp 2802indicates the position of the last pulse, and is determined by therecording mark length and the length of the following space. Forexample, if the mark length is 3T and the following space is 3T, Telp is“q.”

The values a to af in these recording compensation tables are determinedto achieve optimum recording signal quality in each layer.

The recording controller 2715 stores these recording compensation tablesas lookup tables used to set the recording compensation value optimizedfor the recording layer identified by the convergence detector 2712.

By thus setting the recording power and recording compensation tablesoptimized for each recording layer, this embodiment of the inventionimproves recording and playback signal characteristics in the writabledata area, and significantly improves the reliability of an optical discwith plural data recording layers.

This embodiment is further configured to read and write the secondrecording layer through the first recording layer. If when recording thesecond layer, for example, the phase of the first layer directly below(that is, between the laser and second layer) where the second layer isrecorded is blank (that is, only crystalline phase), the first layertransmittance is 50% as shown in FIG. 3. However, if the interveningfirst layer is partially or completely recorded, transmittance increasesin accordance with the area of the recorded tracks in the first layerthrough which the light spot passes to reach the second layer.

As described above, an optical disc drive according to the presentinvention can identify which of plural recording layers on the opticaldisc the light spot is focused on irrespective of whether the data areais recorded or blank. Both recording and playback signal quality canthus be improved in the data area of plural recording layers, and thereliability of an optical disc having plural recording layers can thusbe significantly improved.

Embodiment 13

FIG. 31 is a graph showing the relationship between recording markdensity in the first layer and Strehl ratio calculations in the secondlayer using a wavelength of 660 nm and 0.6 NA. The x-axis in FIG. 31shows the recording mark density. A recording mark density of 0indicates a blank (unrecorded) state. It will be known from FIG. 31 thatas the recording density of the first layer increases, the Strehl numberdecreases. When the Strehl number decreases, beam strength at the secondlayer drops proportionately to the Strehl ratio if the semiconductorlaser emission power is the same, and it is therefore necessary toincrease semiconductor laser emission power.

It is therefore possible to improve playback signal quality from theoptical disc by setting the peak power and bias power levels used torecord to the second layer of the optical disc according to the markdensity of the first layer.

The configuration of a recording power learning area is described nextwith reference to FIG. 34. FIG. 34 shows the configuration of an opticaldisc with a first layer 3401 on the side to which the light spot isincident, and a second layer 3402 on which the light spot is focusedafter passing through the first layer. The first layer 3401 and secondlayer 3402 are concentrically bonded parallel to each other.

Learning areas 3403 are disposed at both the inside and outsidecircumference parts of the first layer 3401, and learning areas 3404 arelikewise disposed at the inside and outside circumference parts of thesecond layer 3402.

User data recording areas 3405 and 3406 for writing user data aredisposed to the first layer and second layer, respectively, between theinside and outside circumference areas.

The learning areas of the first and second layers are located atsubstantially the same positions from the disc center. Methods fordetermining the second layer recording power for each of the followingthree first layer states are described next below.

-   (1) first layer learning area has a blank area-   (2) first layer learning area is partially recorded-   (3) first layer learning area is completely recorded

A method for determining the second layer recording power settings when(1) the entire learning area of the first layer is blank is describedfirst below with reference to the flow chart in FIG. 32.

If the first layer learning area is blank or it is known that there is ablank area in the first layer learning area, the optical head seeks theblank learning area.

The light spot is then focused and tracked on the second layer throughthe blank learning area of the first layer. The second layer recordingpower levels are thus learned after first confirming that the firstlayer is blank. There are various ways of determining the recordingpower, one of which is the 3T mark and space method described above inthe twelfth embodiment.

The recording power levels learned for recording to the second layerwhen the first layer is blank are then stored in memory where the peakpower in a land track is Ppl0, bias power in a land track is Pbl0, peakpower in a groove track is Ppg0, and bias power in a groove track isPbg0. It should be noted that while the recording power is learned andstored for the peak power and bias power in this example, other powerlevels can obviously be learned and stored.

Next, the light spot is focused and tracked to the learning area of thefirst layer. Dummy data is recorded to a specific part of the firstlayer learning area in order to convert it from a blank to a recordedstate. Next, the light spot is focused and tracked to the second layerin the area where this dummy data was recorded. The recording powerlevels for the second layer are thus learned after confirming that thefirst layer has been recorded.

The recording power levels learned for recording to the second layerwhen the first layer is not blank are then stored in memory where thepeak power in a land track is Ppl1, bias power in a land track is Pbl1,peak power in a groove track is Ppg1, and bias power in a groove trackis Pbg1. It should be noted that while the recording power is learnedand stored for the peak power and bias power in this example, otherpower levels can obviously be learned and stored.

A method for determining the second layer recording power settings when(2) the first layer learning area is partially recorded is describednext below with reference to the flow chart in FIG. 32.

If part of the first layer learning area is already recorded, theoptical head seeks the first layer learning area and the light spot isthen focused and tracked on the first layer.

After confirming that the light spot is focused on the learning area inthe first layer, data in a specific part of the first layer learningarea is erased so that it is again blank (has no data recorded thereto).The light spot is then focused and tracked on the second layer throughthis blank learning area of the first layer. The second layer recordingpower levels are thus learned after first confirming that the firstlayer is blank. There are various ways of determining the recordingpower, one of which is the 3T mark and space method described above.

The recording power levels learned for recording to the second layerwhen the first layer is blank are then stored in memory where the peakpower in a land track is Ppl0, bias power in a land track is Pbl0, peakpower in a groove track is Ppg0, and bias power in a groove track isPbg0. It should be noted that while the recording power is learned andstored for the peak power and bias power in this example, other powerlevels can obviously also be learned and stored.

Next, the light spot is focused and tracked to the learning area of thefirst layer. Dummy data is recorded to a specific part of the firstlayer learning area in order to convert it from a blank to a recordedstate. Next, the light spot is focused and tracked to the second layerin the area where this dummy data was recorded. The recording powerlevels for the second layer are thus learned after confirming that thefirst layer has been recorded.

The recording power levels learned for recording to the second layerwhen the first layer is not blank are then stored in memory where thepeak power in a land track is Ppl1, bias power in a land track is Pbl1,peak power in a groove track is Ppg1, and bias power in a groove trackis Pbg1. It should be noted that while the recording power is learnedand stored for the peak power and bias power in this example, otherpower levels can obviously be learned and stored.

A method for determining the second layer recording power settings when(3) all of the first layer learning area has been recorded is describednext below with reference to the flow chart in FIG. 32.

If all of the first layer learning area is already recorded, the opticalhead seeks the first layer learning area and the light spot is thenfocused and tracked on the first layer.

After confirming that the light spot is focused on the learning area inthe first layer, data in a specific part of the first layer learningarea is erased so that it is again blank (has no data recorded thereto).The light spot is then focused and tracked on the second layer throughthis blank learning area of the first layer. The second layer recordingpower levels are thus learned after first confirming that the firstlayer is blank. There are various ways of determining the recordingpower, one of which is the 3T mark and space method described above.

The recording power levels learned for recording to the second layerwhen the first layer is blank are then stored in memory where the peakpower in a land track is Ppl0, bias power in a land track is Pbl0, peakpower in a groove track is Ppg0, and bias power in a groove track isPbg0. It should be noted that while the recording power is learned andstored for the peak power and bias power in this example, other powerlevels can obviously also be learned and stored.

Next, the light spot is focused and tracked to the learning area of thefirst layer. When it is known that a particular part of the first layerlearning area is not blank, the optical head directly seeks thatrecorded area. Next, the light spot is focused and tracked to the secondlayer through the recorded part of the first layer learning area. Therecording power levels for the second layer are thus learned afterconfirming that the first layer has already been recorded.

The recording power levels learned for recording to the second layerwhen the first layer is not blank are then stored in memory where thepeak power in a land track is Ppl1, bias power in a land track is Pbl1,peak power in a groove track is Ppg1, and bias power in a groove trackis Pbg1. It should be noted that while the recording power is learnedand stored for the peak power and bias power in this example, otherpower levels can obviously be learned and stored.

Methods (1), (2) and (3) above detect the initial state of the firstlayer learning area, but this initial state detection step can beeliminated to simplify the system. In this case the recording powerlevels for the second layer are determined using the above method (2)based on the assumption that part of the first layer learning area isnot blank.

Recording to the user data area in the second layer is described next.If the part of the first layer the light spot passes through in order torecord to the user data area of the second layer is largely blank, therecording power can be set to peak power Ppl0 and bias power Pbl0 in theland tracks, and to peak power Ppg0 and bias power Pbg0 in the groovetracks.

If the part of the first layer the light spot passes through in order torecord to the user data area of the second layer is largely recorded,the recording power can be set to peak power Ppl1 and bias power Pbl1 inthe land tracks, and to peak power Ppg1 and bias power Pbg1 in thegroove tracks.

If the part of the first layer the light spot passes through in order torecord to the user data area of the second layer contains a mixture ofrecorded and blank areas, or if the recording mark density is betweenblank and recorded states, the recording power can be set to peak powerPpl0 or Ppl1 and bias power Pbl0 or Pbl1 in the land tracks, and to peakpower Ppg0 or Ppg1 and bias power Pbg0 or Pbg1 in the groove tracks.

Alternatively, if the part of the first layer the light spot passesthrough in order to record to the user data area of the second layercontains a mixture of recorded and blank areas, or if the recording markdensity is between blank and recorded states, the recording power can beset to an extrapolated peak power Ppl2 between Ppl0 and Ppl1 andextrapolated bias power Pbl2 between Pbl0 and Pbl1 in the land tracks,and to extrapolated peak power Ppg2 between Ppg0 and Ppg1 andextrapolated bias power Pbg2 between Pbg0 and Pbg1 in the groove tracks.

These power levels can be extrapolated by simply obtaining the averagesas shown below.(Ppl0+Ppl1)/2(Pbl0+Pbl1)/2(Ppg0+Ppg1)/2(Pbg0+Pbg1)/2

Alternatively, the learned power levels can be weighted and then addedto obtain the extrapolated levels as shown below.Ppl0*y1+Ppl1*y2where y1 and y2 are real numbers such that y1+y2=1, and are determinedaccording to the recording mark density of the first layer through whichthe light spot passes.

It should be noted that while the land track peak power is consideredhere, the same operation can be applied to the land track bias power andthe groove track peak power and bias power levels.

By setting the recording power levels for the second layer according tothe recording mark density in the first layer through which the lightspot passes when recording to the second layer, recording and playbacksignal quality can be improved in the data areas of plural datarecording layers, and the reliability of an optical disc having pluraldata recording layers can be significantly improved.

FIG. 31 is a graph showing the relationship between recording markdensity in the first layer and Strehl ratio calculations in the secondlayer using a wavelength of 660 nm and 0.6 NA. The x-axis in FIG. 31shows the recording mark density. A recording mark density of 0indicates a blank (unrecorded) state. It will be known from FIG. 31 thatas the recording density of the first layer increases, the Strehl numberdecreases. When the Strehl number decreases, beam strength at the secondlayer drops proportionately to the Strehl ratio if the semiconductorlaser emission power is the same, and it is therefore necessary toincrease semiconductor laser emission power. Because semiconductor laseremission power differs, playback signal quality from the optical disccan be improved by determining the recording compensation tables forrecording to the second layer of the disc according to the mark densityof the first layer.

Methods for determining the second layer recording power for each of thefollowing three first layer states are described next below.

-   (1) first layer learning area has a blank area-   (2) first layer learning area is partially recorded-   (3) first layer learning area is completely recorded A method for    determining the second layer recording compensation tables when (1)    the entire learning area of the first layer is blank is described    first below with reference to the flow chart in FIG. 33.

If the first layer learning area is blank or it is known that there is ablank area in the first layer learning area, the optical head seeks theblank learning area.

The light spot is then focused and tracked on the second layer throughthe blank learning area of the first layer. The second layer recordingcompensation table is thus learned after first confirming that the firstlayer is blank. There are various ways of determining the recordingcompensation table, one of which is the minimum jitter method.

The recording compensation tables learned for recording to the secondlayer when the first layer is blank are then stored in memory as landtrack recording compensation table Tl0 and groove track recordingcompensation table Tg0. The recording compensation tables referred tohere and below are the values a to af in the recording compensationtables described above, and tables Tl0 and Tg0 are the respectivecollections of the values a to af.

While the recording compensation tables define four recordingcompensation levels, the invention shall not be so limited and adifferent number of compensation levels can be used.

Next, the light spot is focused and tracked to the learning area of thefirst layer. Dummy data is recorded to a specific part of the firstlayer learning area in order to convert it from a blank to a recordedstate. Next, the light spot is focused and tracked to the second layerin the area where this dummy data was recorded. After thus confirmingthat the first layer has been recorded, the recording compensationtables for the second layer are learned. The results are then stored inmemory as land track recording compensation table Tl1 and groove trackrecording compensation table Tg1.

A method for determining the second layer recording compensation tableswhen (2) the first layer learning area is partially recorded isdescribed next below with reference to the flow chart in FIG. 33.

If part of the first layer learning area is already recorded, theoptical head seeks the first layer learning area and the light spot isthen focused and tracked on the first layer.

After confirming that the light spot is focused on the learning area inthe first layer, data in a specific part of the first layer learningarea is erased so that it is again blank (has no data recorded thereto).The light spot is then focused and tracked on the second layer throughthis blank learning area of the first layer. The second layer recordingcompensation table is thus learned after first confirming that the firstlayer is blank. There are various ways of determining the recordingcompensation tables, one of which is the minimum jitter method.

The recording compensation tables learned for recording to the secondlayer when the first layer is blank are then stored in memory as landtrack recording compensation table Tl0 and groove track recordingcompensation table Tg0.

Next, the light spot is focused and tracked to the learning area of thefirst layer. Dummy data is recorded to a specific part of the firstlayer learning area in order to convert it from a blank to a recordedstate. Next, the light spot is focused and tracked to the second layerin the area where this dummy data was recorded. After thus confirmingthat the first layer has been recorded, the recording compensationtables for the second layer are learned. The results are then stored inmemory as land track recording compensation table Tl1 and groove trackrecording compensation table Tg1.

A method for determining the second layer recording compensation tableswhen (3) the first layer learning area is completely recorded isdescribed next below with reference to the flow chart in FIG. 33.

If all of the first layer learning area is already recorded, the opticalhead seeks the first layer learning area and the light spot is thenfocused and tracked on the first layer.

After confirming that the light spot is focused on the learning area inthe first layer, data in a specific part of the first layer learningarea is erased so that it is again blank (has no data recorded thereto).The light spot is then focused and tracked on the second layer throughthis blank learning area of the first layer. The second layer recordingcompensation tables are then learned after first confirming that thefirst layer is blank. There are various ways of determining therecording compensation tables, one of which is the minimum jittermethod.

The recording compensation tables learned for recording to the secondlayer when the first layer is blank are then stored in memory as landtrack recording compensation table Tl0 and groove track recordingcompensation table Tg0.

Next, the light spot is focused and tracked to the learning area of thefirst layer. When it is known that a particular part of the first layerlearning area is not blank, the optical head directly seeks thatrecorded area. Next, the light spot is focused and tracked to the secondlayer through the recorded part of the first layer learning area. Afterthus confirming that the first layer is not blank, the second layerrecording compensation tables are learned. The results are then storedin memory as land track recording compensation table Tl1 and groovetrack recording compensation table Tg1.

Methods (1), (2) and (3) above detect the initial state of the firstlayer learning area, but this initial state detection step can beeliminated to simplify the system. In this case the recordingcompensation tables for the second layer are determined using the abovemethod (2) based on the assumption that part of the first layer learningarea is not blank.

Recording to the user data area in the second layer is described next.If the part of the first layer the light spot passes through in order torecord to the user data area of the second layer is largely blank, landtrack recording compensation table Tl0 and groove track recordingcompensation table Tg0 are used.

If the part of the first layer the light spot passes through in order torecord to the user data area of the second layer is largely recorded,land track recording compensation table Tl1 and groove track recordingcompensation table Tg1 are used.

If the part of the first layer the light spot passes through in order torecord to the user data area of the second layer contains a mixture ofrecorded and blank areas, or if the recording mark density is betweenblank and recorded states, either land track recording compensationtable Tl0 or Tl1, and either groove track recording compensation tableTg0 or Tg1, are used.

Alternatively, if the part of the first layer the light spot passesthrough in order to record to the user data area of the second layercontains a mixture of recorded and blank areas, or if the recording markdensity is between blank and recorded states, an extrapolated table Tl2between land track recording compensation table Tl0 and Tl1, and anextrapolated table Tg2 between groove track recording compensation tableTg0 and Tg1, can be used.

Table extrapolation is described next with reference to FIG. 36. In FIG.36 reference numeral 3605 shows exemplary land track recordingcompensation tables Tl0 learned when the first layer is blank, andreference numeral 3606 shows exemplary land track recording compensationtables Tl1 learned when the first layer is recorded (not blank).

The tables shown in block 3605 in FIG. 36 define the 36 values from A1to Af1 corresponding to various mark and space combinations at the firstpulse in the pulse train. The tables shown in block 3606 define the 36values from A2 to Af2 corresponding to various mark and spacecombinations at the last pulse in the pulse train.

The tables define compensation values for the same mark and spacecombinations. For example, A1 and A2 define compensation values for a 3Tspace and 3T mark combination but for different first layer conditions.

Extrapolated tables can be calculated by obtaining the average of thevalues at the same mark and space combination positions in the tables asshown below.(A1+A2)/2(B1+B2)/2. . .(Af1+Af2)/2

Alternatively, the tables can be extrapolated by weighting and thenadding the values as shown below.A1*z1+A2*z2B1*z1+B2*z2. . .Af1*z1+Af2*z2where z1 and z2 are real numbers such that z1+z2=1, and are determinedaccording to the recording mark density of the first layer through whichthe light spot passes.

It should be noted that while the land track compensation tables Tl0 andTl1 are considered here, the same operation can be applied to the groovetrack tables.

By setting recording compensation tables for the second layer accordingto the recording mark density in the first layer through which the lightspot passes when recording to the second layer, recording and playbacksignal quality can be improved in the data areas of plural datarecording layers, and the reliability of an optical disc having pluraldata recording layers can be significantly improved.

Embodiment 14

A fourteenth embodiment of the present invention is described next withreference to FIG. 35, which shows the configuration of an optical discin the present embodiment.

The optical disc shown in FIG. 35 has a first layer substrate 3501,first layer user data recording area 3502, first layer learning areas3503, recording-prohibited areas 3504 disposed in the first layerlearning area 3503, and read-only area 3505 provided on the insidecircumference side of the first layer learning area at the insidecircumference of the disc.

The recording-prohibited areas 3504 are described next. When recordingto the second layer, the recording power or recording compensation tableoptimized for the second layer differs according to the recording markdensity in the first layer through which the light spot passes in orderto record to the second layer. It is therefore necessary to learn therecording power levels or recording compensation tables that are bestfor a particular recording mark density.

Providing recording-prohibited areas 3504 as shown in FIG. 35 enablesthe optimum settings for a blank first layer to be learned more quicklywhen recording the second layer. If a recording-prohibited area 3504 isnot provided, it is necessary as described above to determine whether

-   (1) the first layer learning area has a blank area,-   (2) the first layer learning area is partially recorded, or-   (3) the first layer learning area is completely recorded.

If, however, it is known that there is a blank area in the first layer,learning can follow the blank area conditions in the flow chart shown inFIG. 32. It is therefore not necessary to erase an area in the firstlayer in order to create a blank area, and the learning time isshortened accordingly.

Embodiment 15

A fifteenth embodiment of the present invention is described next withreference to FIG. 35, which shows the configuration of an optical discin the present embodiment.

Information identifying the type of optical disc is preprinted in theread-only area 3505 in the formed of modulated prepits. The locations ofthe first and last radial positions of the recording-prohibited areas3504 are also recorded in the read-only area 3505. Alternatively, thestart and end addresses of the recording-prohibited areas 3504 arerecorded.

The disc drive can therefore know by reading the read-only area 3505that there is an area on the disc that cannot be recorded to, and canknow that the first layer is blank when the light spot passes throughthe recording-prohibited area 3504 of the first layer when learning therecording power or recording compensation tables in the learning area ofthe second layer.

It is therefore possible to omit the steps for erasing data in the firstlayer in order to confirm a blank area in the first layer when learningthe recording power or recording compensation tables for the secondlayer, and the learning time can be shortened accordingly.

By thus setting recording power levels or recording compensation tablesoptimized for each recording layer, recording and playback signalcharacteristics can be improved in the data areas of plural datarecording layers, and the reliability of an optical disc having pluraldata recording layers can be significantly improved.

An optical disc, optical disc drive, and optical disc playback methodaccording to the present invention can thus identify which of pluraldata recording layers the light spot is focused on whether or not datais recorded to a data area of an optical disc having plural datarecording layers. The reliability of an optical disc having plural datarecording layers can therefore be significantly improved.

Although the present invention has been described in connection with thepreferred embodiments thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications willbe apparent to those skilled in the art. Such changes and modificationsare to be understood as included within the scope of the presentinvention as defined by the appended claims, unless they departtherefrom.

1. An optical disc drive for detecting address information from an optical disc including a plurality of data layers, and then starting reproduction, the optical disc drive comprising: a laser driver operable to drive a semiconductor laser; a converging unit operable to selectively converge a light beam on each of the plurality of data layers of the optical disc, the light beam being light output from the semiconductor laser driven by said laser driver; a focus controller operable to control a focal position of a convergence point of the light beam converged by said converging unit on the optical disc; a tracking controller operable to position the convergence point of the light beam converged by said converging unit on a track of the optical disc; a photodetector operable to detect reflection of the light beam from the optical disc; and a convergence detection unit operable to detect convergence of the light beam emitted to one of the plurality of data layers of the optical disc before the optical disc drive detects the address information, wherein the optical disc drive controls said laser driver based on an output from said convergence detection unit, and sets light beam emission power when reading from the optical disc separately for each of the plurality of data layers of the optical disc before the address information is detected.
 2. An optical disc drive as described in claim 1, wherein said photodetector detects peak and valley prepits preformed to a plurality of locations in one revolution of continuous tracks on the optical disc, and the output from said convergence detection unit is a result of said photodetector detecting the peak and valley prepits.
 3. An optical disc drive as described in claim 1, wherein said photodetector detects guide grooves preformed on the optical disc, and the output from said convergence detection unit is a result of said photodetector detecting the guide grooves.
 4. An optical disc drive as described in claim 1, wherein said photodetector detects a recording signal written to a data area of the optical disc, and the output from said convergence detection unit is a result of said photodetector detecting the recording signal.
 5. An optical disc drive for detecting address information from an optical disc including a plurality of data layers, and then starting reproduction, the optical disc drive comprising: a laser driver operable to drive a semiconductor laser; a converging unit operable to selectively converge a light beam on each of the plurality of data layers of the optical disc, the light beam being light output from the semiconductor laser driven by said laser driver; a focus controller operable to control a focal position of a convergence point of the light beam converged by said converging unit on the optical disc; a tracking controller operable to position the convergence point of the light beam converged by said converging unit on a track of the optical disc; a photodetector operable to detect reflection of the light beam from the optical disc; and a convergence detection unit operable to detect convergence of the light beam before the optical disc drive detects the address information, wherein the optical disc drive controls said laser driver based on an output from said convergence detection unit, and sets light beam emission power when recording to the optical disc separately for each of the plurality of data layers of the optical disc before the address information is detected.
 6. An optical disc drive as described in claim 5, wherein the optical disc comprises: a first substrate having a first data layer; a transparent reflection layer formed on the first data layer of the first substrate; a second substrate having a second data layer having a recordable film for recording and reproducing information; and an adhesive layer bonding the first substrate and the second substrate with the first data layer and the second data layer facing each other, and wherein the optical disc drive reads information recorded to the first data layer and the second data layer through the first substrate.
 7. An optical disc drive as described in claim 5, wherein said photodetector detects a prewritten signal from a read-only area of the optical disc, and the output from said convergence detection unit is a result of said photodetector detecting the prewritten signal.
 8. An optical disc drive as described in claim 5, wherein said photodetector detects peak and valley prepits preformed to a plurality of locations in one revolution of continuous tracks of the optical disc, and the output from said convergence detection unit is a result of said photodetector detecting the peak and valley prepits.
 9. An optical disc drive as described in claim 5, wherein said photodetector detects guide grooves preformed on the optical disc, and the output from said convergence detection unit is a result of said photodetector detecting the guide grooves.
 10. An optical disc drive as described in claim 5, wherein said photodetector detects a recording signal written to a data area of the optical disc, and the output from said convergence detection unit is a result of said photodetector detecting the recording signal.
 11. An optical disc drive for detecting address information from an optical disc including a plurality of data layers, and then starting recordation or reproduction, the optical disc drive comprising: a laser driver operable to drive a semiconductor laser; a converging unit operable to selectively converge a light beam on each of the plurality of data layers of the optical disc, the light beam being light output from the semiconductor laser driven by said laser driver; a focus controller operable to control a focal position of a convergence point of the light beam converged by said converging unit on the optical disc; a tracking controller operable to position the convergence point of the light beam converged by said converging unit on a track of the optical disc; a photodetector operable to detect reflection of the converged light beam from the optical disc; an equalization controller operable to control equalization characteristics of an RF signal for output from the optical disk drive; and a convergence detection unit operable to detect convergence of the light beam emitted to one of the plurality of data layers of the optical disc, wherein the optical disc drive sets the equalization characteristics of the RF signal for output from the optical disk drive for each of the plurality of data layers based on an output from said convergence detection unit.
 12. An optical disc drive as described in claim 11, wherein said photodetector detects peak and valley prepits preformed to a plurality of locations in one revolution of continuous tracks of the optical disc, and the detection value output from said convergence detection unit is a result of said photodetector detecting the peak and valley prepits.
 13. An optical disc drive as described in claim 11, wherein said photodetector detects guide grooves preformed on the optical disc, and the output from said convergence detection unit is a result of said photodetector detecting the guide grooves.
 14. An optical disc drive as described in claim 11, wherein said photodetector detects a recording signal written to a data area of the optical disc, and the output from said convergence detection unit is a result of said photodetector detecting the recording signal. 